The invention relates to an electrical circuit for conveying on/off type information, in particular for an application to railways.
In a train, numerous on/off type signals indicating the states of various parameters or pieces of equipment are conveyed, for example, to an automatic electronic control circuit, or to an instrument and control panel.
For example, such signals are representative of the state of a circuit breaker or of the open or closed position of a door giving passengers access.
These signals need to be carried with a high degree of security and availability, which makes computer-type low-current links unsuitable.
One solution now in use consists in connecting a closed loop electrical circuit to the two terminals of a battery, the circuit comprising in series: at least one switch associated with the state of the member to be monitored; a resistor; and an electrically isolated link connected to the device that is the destination for the information contained in the signal, for example the automatic electronic control circuit or the instrument and control panel.
The open or closed position of the switch is representative of the state of a parameter or of a piece of equipment. When the switch is closed, current of magnitude that is limited by the resistor flows in the circuit. When the switch is open, no current passes. The presence or the absence of said current is transformed by the electrically isolated link into on/off information that is communicated to the electronic circuit.
In general, a train has a plurality of such circuits connected to the terminals of the same battery.
Since switches tend to become oxidized, some minimum current of the order of a few tens of milliamps must pass through each of the switches in order to clean them.
This current is consumed and lost in the resistor.
Furthermore, the power dissipated in the resistor by the Joule effect produces heat which must be removed.
One solution would be to use fans.
However, at present, the use of fans for cooling electronic circuits on board trains is avoided or even banned for reasons of reliability, since a fan has mechanical components that might become jammed, cease moving, and in general, give rise to a breakdown.
The reliability of electrical and electronic components decreases significantly when ambient temperature increases, so it is desirable to produce as little heat as possible.
Furthermore, since the battery generally powers a plurality of other circuits and equipment, the voltage it delivers varies over time depending on the load across its terminals.
The magnitude of the current in the circuit thus also varies, in proportion to the state of charge of the battery.
Consequently, to obtain the minimum current required for cleaning the switches, it is necessary to consume a large amount of extra current (and thus power) during certain periods in the operation of the circuit. The additional heat which is produced further complicates the problem of removing this heat.
The quantity of heat dissipated increases with the number of switches and the amount of information to be transmitted.
The invention seeks to reduce the above-mentioned drawbacks of the prior art.
The invention thus seeks to convey on/off type information with a high degree of reliability and of availability, while nevertheless reducing the amount of heat dissipated by the Joule effect.
The invention thus provides an electrical circuit for transmitting the state of a parameter or of a piece of equipment and designed to be connected to the terminals of a power supply battery, the circuit comprising:
an isolated link between said electrical circuit and an output for sending an item of state information; and
a switch whose open or closed position is representative of the state information and determines whether or not a current flows in said electrical circuit;
the electrical circuit transmitting state information from the switch to the output via the isolated link;
the electrical circuit comprising means for regulating the magnitude of the current flowing through the switch, said means comprising switch means, connections between component elements of the electrical circuit and comprising inductive energy storage means in series with the switch and capacitive energy storage means which, under steady conditions, alternate between constituting means for storing and means for restoring a fraction of the energy of said electrical circuit, depending on the alternating state of said connections between the component elements of the electrical circuit, as determined by the switch means.
According to other characteristics of this electrical circuit:
the isolated link is connected in series with the switch;
the means for regulating the current through the switch further include means for monitoring a magnitude that is characteristic of the state of the electrical circuit and for controlling the switch means to alternate connections between the elements constituting the electrical circuit as a function of the state of said electrical circuit;
the switch means for switching the connections between the elements constituting the electrical circuit establish at least the following connections in an alternation: the inductive energy storage means, the switch, the power supply battery, and the capacitive energy storage means in series in a closed loop during a first stage, under steady conditions, in which the inductive energy storage means restore a quantity of energy which is stored in the capacitive energy storage means; and the inductive energy storage means, the switch, and the capacitive energy storage means in series in a closed loop during a second stage, under steady conditions, in which the capacitive energy storage means restore a quantity of energy which is stored by the inductive energy storage means; the polarity of the connections between the inductive energy storage means and the capacitive energy storage means being inverted between the first and second stages.
the inductive energy storage means and the capacitive energy storage means comprise respectively: an inductor in series with the switch; and a capacitor; first and second parallel-connected branches in series with the switch and the inductor, and includes a resistor in parallel with the switch and the inductor, and connected to a point of the second branch, the capacitor being connected in the second branch; and the means for switching the connections comprises means for directing the current flowing through the switch and the inductor through the first and second branches in alternation;
the isolated link is connected in the first branch;
the isolated link is connected in series with the capacitor in the second branch;
the isolated link is connected in series with the resistor;
the period during which the current flowing through the switch and the inductor flows successively through the first branch and then through the second branch, and the duty ratio which is equal to the time said current flows through the first branch divided by said period, are respectively fixed and variable, and are determined by the means for monitoring the magnitude characteristic of the state of the electrical circuit and for periodically controlling the switch means;
the means for directing the current passing through the switch and the inductor alternately through the first branch and through the second branch comprise a controlled switch connected in the first branch and a diode connected in the second branch between firstly one of the two junctions between the first and second branches, and secondly the connection point between the resistor and the second branch, the capacitor lying between the other one of said two junctions between the first and second branches, and the connection point of the resistor and the second branch;
the isolated link is connected in series with the diode;
the isolated link consists in an optocoupler;
the isolated link consists in a transformer;
the primary winding of said transformer also forms at least a portion of the inductive energy storage means;
said means for monitoring a magnitude characteristic of the state of the electrical circuit and for periodically controlling the switch means also form the isolated link and for this purpose are provided with said outlet for sending the information and are suitable for sending this information on the basis of processing said characteristic magnitude, in particular on the basis of the duty ratio;
the peak value during a period of the current flowing through the switch constitutes said magnitude characteristic of the state of the electrical circuit;
the potential at the point where the resistor is connected to the second branch constitutes said magnitude characteristic of the state of the electrical circuit;
the voltage across the terminals of the resistor constitutes said magnitude characteristic of the state of the electrical circuit;
it further includes means for testing correct operation thereof, independently of the position of the state switch;
the means for testing correct operation of the electrical circuit include:
a controlled test switch and a test battery connected in a first series circuit which is in turn connected in parallel with a second series circuit including the state switch and a location for connecting the power supply battery; and
an automatic test unit connected to the control terminal of the controlled test switch and to the outlet for transmitting state information;
the means for testing correct operation of the electrical circuit include:
a controlled test switch connected in parallel with the state switch, the assembly being connected in series with a location for connecting the power supply battery that is also to operate as a test battery; and
an automatic test unit connected to the control terminal of the controlled test switch and to the outlet for transmitting state information;
the automatic test unit, also connected to the means for monitoring a magnitude that is characteristic of the state of the electrical circuit and for operating the switch means of the connections in alternation, is suitable for holding said switch means in at least one current cut-off position in said electrical circuit;
the means for testing correct operation of the electrical circuit include at least one protective diode connected in series with the state switch to block current coming from the controlled test switch; and
the means for testing correct operation of the electrical circuit include another protective diode connected in series with the controlled test switch to block current coming from the state switch.
The invention also provides an electrical system for transmitting a plurality of items of state information, the system comprising a battery and a plurality of electrical circuits as defined above, each serving to transmit one item of state information and all connected in parallel across the terminals of said battery.
According to other characteristics of this electrical system, it is mounted on board a railway train, each switch being associated with a member or with a piece of equipment of said railway train, to monitor the state or the position thereof.